Tuneability of Sm(1 − x)CexFeO3 ± λ perovskites: Thermal stability and electrical conductivity

Trimetallic perovskite oxides, Sm(1 − x)CexFeO3 ± λ (x = 0–0.05), were prepared by thermal decomposition of amorphous citrate precursors followed by calcinations. The material properties of the substituted perovskites were characterized by X-ray diffraction (XRD), X-ray florescence spectroscopy (XRF), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The doped materials exhibited a single perovskite phase in air up to 1350 °C and have specific surface areas in the range of 2.696–8.665 m2/g. In reducing atmosphere (5%v/vH2/N2), the unsubstituted perovskite (x = 0) decomposed into two phases while the ceria stabilized materials (x = 0.01, x = 0.03, x = 0.05) remained in a single phase as revealed by XRD analysis. Their conductivities were measured by the four point probe method in air and in dilute hydrogen (5%v/vH2/N2) separately. The ceria substituted materials show increased stability versus reduction and phase separation for a wide temperature range (up to 1000 °C). Although undoped SmFeO3 has higher conductivity under oxidizing conditions than ceria doped SmFeO3 due its p-type nature, the situation is reversed under reducing conditions. The ceria substituted perovskites (Sm(1 − x)CexFeO3 ± λ, x = 0–0.05) showed higher conductivity in reducing than in oxidizing conditions, suggesting that ceria doping at the A-site has changed the SmFeO3 from p-type to n-type semi-conducting behavior.